test: have ./check tail the test.py log file on failure

For each subplot, if running the test program fails, the last 100
lines of the log file is output. For the reference.md subplot, the
last 100 lines of the log file for the test program from the
referenced subplot is output.

This makes it easier to debug failures in CI.

Sponsored-by: author

1 files changed, 20 insertions, 1 deletions

diff --git a/reference.md b/reference.md
index 09ac659..48e2295 100644
--- a/reference.md
+++ b/reference.md
@@ -1,3 +1,4 @@
+
 # Introduction
 
 This document describes how we guard against accidental breaking
@@ -40,7 +41,25 @@ then command is successful
 #!/bin/bash
 
 set -euo pipefail
-python3 src/test-inner.py --log test-inner.log --env "PATH=$PATH" --env SUBPLOT_DIR=/
+
+N=100
+
+if python3 src/test-inner.py --log test-inner.log --env "PATH=$PATH" --env SUBPLOT_DIR=/
+then
+    exit=0
+else
+    exit="$?"
+fi
+
+if [ "$exit" != 0 ]
+then
+    # Failure. Show end of inner log file.
+
+    echo "last $N lines of test-inner.log:"
+    tail "-n$N" test-inner.log | sed 's/^/    /'
+fi
+
+exit "$exit"
 ~~~